Eddy current testing (ET) is a technique that can be used for nondestructive evaluation (NDE) of conductive components. A coil producing a varying magnetic field can be positioned near the conductive component to induce eddy current in the material. Signal analysis processes for analyzing eddy current response signals to obtain component information have been developed over decades of industrial practice (see, for example, V. S. Cecco, G. Van Drunen, and F. L. Sharp, “Eddy Current Manual”, Volume 1, AECL Report, AECL-7523 Rev 1, (1983), also Cecco, V. S., and Van Drunen, G., “Recognizing the Scope of Eddy Current Testing”, Research Techniques in Nondestructive Testing, Vol. 8, ed., R. S. Sharpe, Academic Press Inc., pp. 269-301 (1985)).
ET was traditionally performed using magnetic fields induced by sinusoidally varying currents. Over time, testing with “pulsed”, also known as “transient” eddy currents (PEC or TEC), has become more prevalent for certain applications. However, traditional ET analysis techniques typically cannot be directly applied to pulsed eddy current signals. As a result, quantitative processes for evaluating various structural parameters such as the probe-to-material distance, material thickness, surface extent of flaws, flaw depth, and other geometric measurements using PEC are needed.
Current PEC analysis techniques typically involve correlating specific features of the PEC signal response, such as the time and rate-of-change of the transition from positive to negative voltage, or maximum signal amplitude, to reference samples having known values of the property to be measured. In this approach, unknown samples are assessed using the specific feature of the response signal, effectively constituting a single-variable calibration. In cases where only one quantity is unknown, the existing process is adequate. However, inspected components often have multiple quantities that vary simultaneously, such as the distance between the probe and conductor surface at a flaw of unknown depth and area. Such cases are not quantified by existing PEC analysis techniques.